The present invention relates to a safety device for a washing system for liquid fuel injectors in gas turbines.
As is known, gas turbines comprise a compressor in which air obtained from the external environment is compressed.
This compressed air passes into a series of combustion chambers which contain one or more burners, into each of which an injector feeds fuel which is mixed with the air in order to form a mixture of air and fuel to be burnt.
Subsequently the burnt gases are conveyed to the turbine, which transforms the enthalpy of the gases burnt in the said combustion chamber into mechanical energy which is available to a user.
In particular, there exist gas turbines which function with xe2x80x9cdual fuelxe2x80x9d, i.e. with two types of fuel, in other words liquid or gaseous.
In this case the turbines are provided with separate injectors for combustion respectively of the gaseous or liquid fuel.
When the turbine is functioning with gaseous fuel, the liquid fuel injector is not fed and therefore it becomes necessary to wash the injectors which are not being used with a flow of inert gas or air. This is in order to prevent intake of mixtures of air and fuel or burnt gases in cases in which there is not a perfect seal upstream from the injector.
In addition, the continuous washing has a beneficial effect of cooling the injectors and eliminates any residual trace of liquid fuel which could cause problems. If in fact liquid fuel remains inside the burner, it could become carbonised owing to the effect of the high temperature and therefore block the injection holes of the injectors.
Advantageously, the continuous washing of the burners can be carried out with the air taken from the outlet of the axial compressor of the turbine, using the pressure difference between the compressor outlet and the interior of the combustion chamber. For this reason the washing is known as xe2x80x9cpassivexe2x80x9d, since use is made of the loss of pressure in the combustion chamber.
Additionally, the system for this washing must be provided with a protection device, so that when the burner is fed with the liquid fuel, the latter cannot flow back through the washing air feed pipe into the compressor discharge box, with the risk of self-ignition and consequent serious structural damage to the turbine.
At present the system is produced using a stop valve on the air feed line, through which a manifold which distributes the air to the various burners is fed.
Each pipe which connects the air manifold to the various burners is then provided with a further stop valve, whereas at the lowest point of the manifold there is provided a drainage valve which is connected to an external system for collection of the drainage products.
When the turbine is functioning with gaseous fuel, the stop valve on the line for feeding air to the manifold and the stop valves on the burners are open, thus permitting washing of the burners. It will be appreciated that in this case the drainage valve remains closed.
On the other hand when the burner is fed with the liquid fuel, the stop valve on the air feed line, which for the sake of simplicity will also be called the feed valve, and the other stop valves, are closed, thus guaranteeing physical separation of the washing air obtained from the axial compressor, from the liquid fuel which is conveyed to the injectors.
In this case the drainage valve is open. By this means any blow-by of liquid fuel caused by breakage or imperfect sealing of a valve is collected in the manifold and discharged from the drainage collection system. This system can also be provided with a visual pilot lamp or other type of signal to indicate the leakage.
However, if this type of system were subjected to substantial leakages of liquid fuel, it would not be possible to guarantee adequate protection against the risk of dangerous self-ignition.
The object of the present invention is thus to eliminate the above-described disadvantages and in particular to provide a safety device for a washing system for liquid fuel injectors in gas turbines, which makes it possible to indicate the presence of leakages efficiently, directly on the control panel of the gas turbine.
Another object of the present invention is to provide a safety device for a washing system for liquid fuel injectors in gas turbines, which is particularly reliable, simple and functional, and has relatively low costs.
Advantageously, this safety device for a washing system for liquid fuel injectors in gas turbines guarantees the collection of leakages or condensation inside the latter, independently from the characteristics of the system downstream.
The characteristics and advantages of a safety device according to the present invention for a washing system for liquid fuel injectors in gas turbines will become more apparent from the following description provided by way of non-limiting example with reference to the attached schematic drawings, in which: